This invention relates to a powder sampling device.
It may be used in particular to take intermittent samples of powder flowing more or less continuously in an industrial process, in order to check the composition or quality, and is particularly advantageous if the volumes must be invariable, fine or are dangerous.
Traditional sampling devices include valves, taps or analogous devices, but they are poorly suited to powders, which can easily penetrate into moving parts and cause them to seize, and providing an efficient seal against leaks of dangerous materials is hard to ensure. Furthermore, it is difficult to adjust the volume that is sampled, with such means.
Another major problem that needs to be resolved to obtain satisfactory samples consist of avoiding stagnation of the powder from an earlier moment in the flow around the sampling device, which would be mixed in with the powder sampled and comprise the reliability of the measurement.
Another problem which could be important consists of avoiding the sampling device from disrupting the flow, which could furthermore lead to the problem mentioned above, of creating a pocket of stagnant powder in front of the device.
The powder sampling device of the document U.S. Pat. No. 4,024,765 comprises: an appended part, generally empty of powders, of a powder flow channel; a reciprocating member traversing a wall of the appended part, and sliding between a first position where a groove in it extends into the appended part and a second position where the groove extends beyond the appended part, the groove being limited by faces where the powder slides or falls; and a flap in the flow channel, moving between a withdrawn position where it has no essential effect on the flow of the powders and an extended position where it directs the flow of the powders into the appended part.
It appears that the flow of the powders passes beside the sampling device in normal conditions, and is not likely to be disrupted by it or to foul it by stagnating powder. In the sampling position, the powder or a portion of it is on the contrary temporarily directed towards the appended part containing the sampling device and fills the reciprocating member groove, which may then be moved to the second position where the volume of the powder contained in the groove is sampled and analysed. In this patent, the reciprocating member is pushed into the appended part when the powder fills it. A powder sample enters the groove, then the reciprocating member is removed and is turned over. The content of the groove then escapes from it entirely. This design may be criticized in that the reciprocating member is moved in a translation and rotation movement, which is complicated, increases the possibility of friction and seizure, and that quite a large volume of powder must fill the appended part for a sample to be taken.
A representative sample of the flow at a specific given time may become impossible.